The present invention relates to a multilayer wiring substrate for use in electronic computer or for various mounting uses.
In the field of mounting module substrate used for enhancing the operation speed of electronic computer, enhancement of the speed of signal transmission is an important problem.
In the prior module substrate, thick film multilayer wiring substrates obtained by forming low-conductivity wiring layers of W, Mo or the like by the ceramics lamination-sintering process have been used predominantly. With the aim of enhancing the signal transmission sped, however, multilayer thin-film wiring substrates prepared by forming an interlaminar insulation film of polyimide resin having a low dielectric constant on a ceramics multilayer wiring substrate and providing a conductor layer of Cu, Al, Au or the like having a high conductivity are watched with interest in the recent time (JP-A 60-143649). However, polyimide resins are generally inferior in adhesive performance and moldability in spite of excellence in high temperature stability, due to which reliability of polyimide-derived articles cannot sufficiently be secured. As a method for improving moldability thereof, there has been disclosed a thermosetting resin composition prepared by adding a bismaleimide compound or the like to a specified polyimide (JP-A 3-205474). There has also been disclosed an adhesive material prepared by adding a thermosetting resin to a polyimide having a low softening point (JP-A 4-227960).
JP-A 9-326556 discloses a technique for manufacturing a multilayer wiring substrate by repeating coating of an organic resin and a heat treatment, formation of through holes and attachment of metallic conductor, and formation of wiring pattern on an organic resin insulating layer.
JP-A 8-181450 discloses a technique for manufacturing a multilayer wiring substrate which comprises laminating a thermosetting polyimide resin having a wiring pattern on an adhesive sheet made of a thermoplastic polyimide resin, followed by heating and contact bonding.
Prior adhesive materials have secured fluidity by using a thermosetting resin composition prepared by adding bismaleimide or the like to a specified polyimide, as a means for improving the adhesiveness to a material to be bonded. However, in such a method, the step of imidating polyamic acid (precursor of polyimide) requires a temperature higher than the polymerization temperature of bismaleimide compound, and at such a high temperature the thermosetting resin such as bismaleimide undergoes a thermal polymerization, as a result of which no sufficient fluidity can be exhibited. Further, the resin mentioned above is apt to absorb water when allowed to stand at ambient temperature, and the absorbed water vaporizes to form gaseous steam in the steps of curing and heat treatment to cause interlaminar swelling, interlaminar peeling, etc.
Further, although an adhesive material prepared by adding a thermosetting resin to a thermoplastic polyimide is excellent in fluidity, it is low in elastic modulus at a temperature higher than the glass transition temperature of thermoplastic polyimide, so that the adhesive material portion softens in the step of soldering of LSI and the like, due to which breakage of wiring, interlaminar swelling, etc. take place. Further, this resin exhibits a great dimensional change at a temperature higher than the glass transition temperature of thermoplastic polyimide used, and the relative position between the wirings extremely changes, and this makes an important trouble in obtaining a wiring of high density and high reliability.